Welcome to the latest issue of the Home Lawn Care Newsletter from UMN Turfgrass Science! We will provide up-to-date information to address all your lawn care tasks at the times when you need to know.
May 15, 2024: Issue 21
Spring lawn care can have a big impact on your lawn’s health for the rest of the year, so make sure you’re setting your lawn up for success with our May tips!
Are white grubs eating your lawn?
White grubs have certainly been gaining more attention in Minnesota lawns within the past several growing seasons. White grubs are larvae of several beetle species like Japanese beetles, masked chafers, and May/June beetles that feed on plant roots. So how do you know if white grubs are affecting your lawn? Signs of white grub damage include irregular patches of dead or dying grass that resemble drought stress. Early signs of a white grub infestation are apparent when an irrigation system has been running or we have had regular rainfall and the drought symptoms are still present. Moderate grub damage involves observing dead or dying turf with little to no roots when pulling on the turf. More severe white grub damage is sometimes not caused by the grubs themselves, but by animals like racoons and skunks turning over the turf to feed on the grubs.
Finding grubs does not mean they have to be controlled. A healthy lawn can withstand some grub infestation, so following best lawn care practices will continue to be the best option for your lawn. We recommend managing for white grubs only when there is visible evidence of damage, or if you know you had severe damage the previous fall. White grubs are most active from May to September, and because of varying life cycles from the multiple beetle species, treating them can be tricky.
If you know you have grub damage in late spring or early summer and the lawn needs to be treated, you should use a curative insecticide containing the active ingredients carbaryl, clothianidin, imidacloprid, thiamethoxam, or trichlorfon. These curative treatments should be stopped if the grubs have entered the pupae phase of their life cycle; at that point, the white grubs have stopped feeding and the treatments won’t work.
If you used a curative treatment last summer or autumn because of a severe white grub infestation, or you know you are likely to have a white grub problem again this year, a preventative treatment containing the active ingredient chlorantraniliprole (trade name GrubEx or Acelepryn) is the best strategy. Preventative white grub treatments can be applied between May and early July and are the most effective white grub control with lower toxicity insecticides. Avoid using neonicotinoid insecticides (clothianidin, imidacloprid, or thiamethoxam) as preventative white grub treatments as these can be translocated to bees and other beneficial insects.
There are several biological insecticides that are marketed to control white grubs in lawns. Baccilus thuringiensis galleriae (trade name: GrubGone) is the only known biological insecticide to work effectively. This product works as a preventative treatment and needs to be applied in advance of a white grub infestation. Bacillus popillae (trade name: Milky Spore) is not effective at controlling white grubs in lawns.
Whether you are using a curative, preventative, or biological insecticide, the product should be applied before an irrigation or rain event with at least half an inch of water. Mowing immediately prior to applying the insecticide can remove flowers from flowering plants in the lawn, thereby reducing the exposure to bees and other pollinators, and can help with delivery of the granular products.
Managing white grubs in turfgrass | Purdue Extension
Japanese beetles in yards and gardens | UMN Extension
Lawn care calendar | UMN Extension
Is your irrigation system up to code?
If you have an irrigation system, late spring is a great time to ensure it is working properly and up to code. In Minnesota, all automated irrigation systems are required to have a bypass moisture sensor installed. The moisture sensors could be a rainfall sensor or a soil moisture sensor, but both work similarly. A moisture sensor is designed to detect recent rainfall events and will instruct the irrigation system to bypass or skip the next scheduled watering.
It is remarkably easy to test to ensure your moisture sensor is installed correctly and working properly. First, schedule your system to run in 20-30 minutes. After locating your moisture sensor, pour a few ounces of water over the sensor prior to when you have your system scheduled to run. If the sensor is working, the system will not run as scheduled. Depending on the model of the irrigation controller, there will likely be an indicator on the controller that the moisture sensor detected “rain” and bypassed that scheduled irrigation timing.
If the moisture sensor failed at delaying the irrigation system from running, or if you know you need a new moisture sensor, consider contacting your local municipality. Many cities in Minnesota have a rebate to offset the cost of a new moisture sensor and/or the cost of a smart irrigation controller. Regardless, most cork-type rainfall sensors are relatively inexpensive, are compatible with most irrigation controllers, and will pay for themselves within the first year through water savings. A functioning moisture sensor not only saves water, but it also helps from over-watering your lawn.
Sec. 103G.298 MN Statutes Landscape Irrigation Systems | Minnesota Legislature
Auditing home lawn irrigation systems | UMN Extension
Water-saving strategies for home lawns | UMN Extension
Help with lawn water conservation | UMN Turfgrass Science
Mowing in the month of May
The month of May certainly attracts a lot of attention for mowing, with media attention ranging from No Mow May to Slow Mow Summer. Spring mowing is a great opportunity to start your lawn off right by making it more resilient for the rest of the growing season.
Adjusting your mowing height is relatively simple, and can have dramatic effects on your lawn. When lawns are maintained to 3.5 inches or higher, they are less stressed and have deeper roots, making them more drought tolerant. A higher mowing height also means the lawn needs to be mowed less frequently. Finally, a higher mowing height also shades out the soil surface, making it more difficult for weed species like crabgrass to germinate and emerge.
What not mowing in May could mean for your lawn | UMN Extension
Slow Mow Summer | UMN Bee Lab
Mowing practices for healthy lawns | UMN Extension
Research highlight
Help needed with bee lawn establishment research!
The University of Minnesota Turfgrass Science team is conducting a brief survey on bee lawn establishment for those who have or are interested in establishing a bee lawn. We would appreciate your valuable input. Your honest feedback will directly guide future research and development of a field guide outlining best practices for successfully establishing a bee lawn. As part of the survey, you can opt-in for a chance to win a $100 gift card via random drawing to a local supplier of bee lawn seed.
Access the survey here: Bee Lawn Establishment. Thank you in advance for your time. Should you have any questions or concerns, reach out to the lead researcher, Michael Barnes, at [email protected].
Events
We will be at these events to answer questions on smart irrigation and lawn care as part of our collaboration with the Metropolitan Council.
- Environmental Fun Fair in Fridley, MN on Saturday, May 18, 2024 from 11:00 a.m. to 2:00 p.m.
- Trista Day in Minnetrista, MN on Saturday, May 18, 2024 from 11:00 a.m. to 2:00 p.m.
- Annual City Open House in Dayton, MN on Wednesday, May 22 from 5:00 p.m. to 7:00 p.m.
- Public Works “Big Trucks” Open House in Edina, MN on Thursday, May 23 from 4:00 p.m. to 7:00 p.m.
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We provide research updates, lawn care tips, info about field days, and more at @UMNTurf.